1. Field of the Invention
The present invention relates to light directing films and light turning films used to redirect light. The present invention also relates to illumination and backlighting devices employing light directing and light turning films, such as wide-area lighting panels, LCD backlights, computer screens, advertising displays, road signs, and the like.
2. Description of Background Art
Conventionally, light directing films employed in backlighting systems include a structured major surface with an array of parallel prisms extending along a direction perpendicular to the plane in which the film is designed to bend the incident light. The prisms are usually arranged side by side and form a plurality of peaks and grooves thus forming a corrugated surface of the film. Applications exist where surface corrugations are unwanted since they are prone to soiling and also complicate surface cleaning. Furthermore, in multi-layer transmissive structures, the corrugations create air pockets between layers which may be unwanted in at least some applications such as those where a monolithic structure is desired. Furthermore, the distributed air pockets represent a layer having a very low refractive index which creates a strong total internal reflection interface. Such interface may prevent certain light rays to pass through the transmissive structure without being reflected, particularly in the applications involving light rays propagating at low angles with respect to the layer surfaces.
It is therefore an object of this invention to provide an improved light directing film having one or more smooth surfaces and eliminating the air spaces associated with surface corrugations of the prior art devices. Other objects and advantages of this invention will be apparent to those skilled in the art from the following disclosure.